1. Field of the Invention
The present invention relates to a thin-film magnetic head comprising a magneto-resistive effect device for reading the magnetic field strength of a magnetic recording medium or the like as signals, and a head gimbal assembly and a magnetic disk system, each comprising that thin-film magnetic head.
2. Explanation of the Prior Art
In recent years, with an increase in the plane recording density of magnetic disk systems, there have been growing demands for improvements in the performance of thin-film magnetic heads. For the thin-film magnetic head, a composite type thin-film magnetic head has been widely used, which has a structure wherein a reproducing head having a read-only magneto-resistive effect device (hereinafter often called the MR device) and a recording head having a write-only induction type magnetic device are stacked together.
The MR device, for instance, includes an AMR device harnessing the anisotropic magneto-resistive effect, a GMR device making use of the giant magneto-resistive effect, and a TMR device taking advantage of the tunnel-type magneto-resistive effect.
Requirements for reproducing heads, among other, are high sensitivity and high output. For reproducing heads meeting such requirements, GMR heads using a spin valve type GMR device have already been mass produced. The reproducing heads using a TMR device, too, are being mass produced so as to meet further improvements in the areal density.
In general, the spin valve type GMR device comprises a nonmagnetic layer, a free layer formed on one surface of that nonmagnetic layer, a fixed magnetization layer formed on another surface of the nonmagnetic layer, and a pinning layer (generally an antiferromagnetic layer) on the side of the fixed magnetization layer facing away from the non-magnetic layer. The free layer has its magnetization direction changing depending on an external magnetic field, and the fixed magnetization layer has its magnetization direction fixed by a magnetic coupling with the pinning layer (antiferromagnetic layer). On each side of the device, there is a bias magnetic field-applying layer formed to apply a bias magnetic field to the free layer, thereby reducing Barkhausen noise.
By the way, common GMR heads used so far in the art have a CIP (current in plane) structure wherein a current for detecting magnetic signals (the so-called sense current) is passed parallel with the plane of each of the layers forming the GMR device (CIP-GMR device). On the other hand, GMR devices having the so-called CPP (current perpendicular to plane) structure wherein the sense current is passed perpendicularly to the plane of each of the layers forming the GMR device (CPP-MR device), too, are now under development as next-generation ones. The aforesaid TMR devices, too, would come under the CPP structure category according to a classification system from the current-passing direction alone.
In the thin-film magnetic head comprising a magneto-resistive effect device of such CPP structure, bias magnetic field-applying layers are located on two sides of the magneto-resistive effect device. Those bias magnetic field-applying layers are operable to apply a so-called longitudinal bias to the device with the result that a given external magnetic filed can be detected while holding back the generation of noises.
Important for the longitudinal bias applied from the bias magnetic field-applying layers to the device is that it acts always consistently to the device while the hard disk device is in operation.
In some cases, however, the performance of the longitudinal bias degrades by reason of stress due to the head disk interface (for instance, head-on collision of the magnetic head and the hard disk, frictional heat that may be generated between the magnetic head and the hard disk, etc.), stress engendered by environmental temperature changes (for instance, fluctuations on the order of −30% to +100%), stress caused by application of magnetic fields from outside, etc.
As the performance of the longitudinal bias degrades, the operation of the reproducing head becomes erratic, ending up with a growing likelihood of malfunction of the hard disk system.
The inventors have already learned that when such erratic operation of the hard disk system is caused by degradation of the bias magnetic field-applying layers, it can substantially go back to normal if the head is removed out by dismantling the hard disk system and a given magnetic field is applied to the bias magnetic field-applying layers to re-magnetize them.
If a re-magnetizer element and electric circuit for re-magnetization are previously built in a magnetic head so that when the bias magnetic field-applying layers of the magnetic head degrade, the re-magnetizer element is actuated to re-magnetize the bias magnetic field-applying layers without dismantling the hard disk system whereby the hard disk system is kept going on, it would be very much beneficial and convenient for both makers and users.
In view of such situations, the present invention has been made with a view to providing a thin-film magnetic head designed such that when the bias magnetic field-applying layers of the head degrade with an increasing error rate of the hard disk system, they can be re-magnetized without dismantling the hard disk system so that it can be kept operating normally.